Time Difference of Arrival Localization Testbed: Development, Calibration, and Automation GRCon 2017

Transcription

1 Time Difference of Arrival Localization Testbed: Development, Calibration, and Automation GRCon 2017 Intelligent Digital Communications Georgia Tech VIP Team 1

2 Overview Introduction IDC Team Stadium Testbed RFSN Control Center (RFSNCC) Why? How? Lab Setup and ToA Calibration Why? Experiment Setup Results 2

3 Introduction Hayden Flinner 3

4 IDC Team Purpose IDC is using software defined radio to enhance spectrum utilization Radio frequency (RF) spectrum is a valuable, limited resource Analyzing how devices interact over RF spectrum allows us to find ways to improve communication in an optimal manner 4

5 Localization Using SDR to develop localization algorithms for Extreme Emitter Density environments (10k-100k people/km2) Recorded terabytes of time synchronous RF IQ data, during football games, at the GT football stadium to assist in algorithm development 5

6 TDoA Localization Assuming time-synced nodes: 1. Record ToAs 2. Take differences 3. Apply Δd = cδt 6

7 Stadium Testbed Hayden Flinner 7

8 RF Sensor Node (RFSN) 8

9 Stadium Testbed RFSN3 RFSN1 9

10 2 Mobile Nodes 10

11 RFSN Control Center (RFSNCC) 11

12 Why RFSNCC? 1. Currently 3 fixed nodes - Goal Logging into each machine and running long series of time-synced record commands is not scalable a. Excessive man-hours b. Error-prone 3. Maintaining RF IQ dataset and associated metadata is tedious 12

13 Initial Plan Upload Schedule RFSN1 Website RFSN

14 Current Site 14

15 Current Site 15

16 Architecture 16

17 Lab Setup and ToA Calibration 17

18 Why a Lab Testbed? Wired nodes provide controlled test environment. Easier to vary cable lengths to test emitter/receiver positions than to run around stadium 18

19 Lab Testbed 19

20 Why Calibration Experiment? Verify that ToAs being recorded are plausible Remove delay inherent to USRPs for more accurate location measurements 20

21 Cramer-Rao Lower Bound (CRLB) CRLB for the standard deviation of the TDoA is theoretic limit on how accurate results can be 21

22 Cramer-Rao Lower Bound (CRLB) Relationship between CRLB and bandwidth 22

23 Q: Does our testbed give us sane results? TDoA -> Btw 1 & 2 Btw 1 & 3 Btw 2 & 3 Mean (ns) Variance (ns2) 4.004E E E-5 Std Dev (ns) 6.327E E E-3 MSE (ns2) 7.241E E E-5 SNR (db) TX sampling rate: 16 Msps RX sampling rate: 16 Msps with 32 MHz master clock. 23

24 A: Yes! Std. Devs. above CRLB! SD of TDoA data plotted against its CRLB at 16 MHz sampling bandwidth Average TDoA over equal length Msp 24

25 Calibration: Testbed Setup Nodes 2, 3, 4, and 5 were passed delayed signal sequence. Nodes 1 and 6 received non-delayed signal sequence. TX: 25 Msps -- RX: 25 Msps, 50 MHz master clock. 25

26 Calibration: Running Experiment LMR-240 cables of known lengths were attached 110 seconds into each recording session. For each node, average ToAs seen during first 100 seconds was subtracted from ToA vector during each recording session. Used magnitude interpolation around the cross-correlation peak value to compute ToA estimate. TX: 25 Msps -- RX: 25 Msps, 50 MHz master clock. 26

27 Time Difference of Arrival over 12 ft LMR240 cable TDoA -> Mean (ns) Variance (ns2) Std Dev (ns) MSE (ns2) Btw 1 & 2 Btw 1 & 3 Btw 1 & 4 Btw 1 & E E E E E E E E-4 Results are of average TDoA vector from four runs Expected delay through 12 ft LMR240 cable is: 12 ft / ft/ns = ns 27

28 Time Difference of Arrival over 50 ft LMR240 cable TDoA -> Mean (ns) Variance (ns2) Std Dev (ns) MSE (ns2) Btw 1 & 2 Btw 1 & 3 Btw 1 & 4 Btw 1 & E E E E E E E E-5 Results are of average TDoA vector from four runs Expected delay through 12 ft LMR240 cable is: 50 ft / ft/ns = ns 28

29 Time Difference of Arrival over 100 ft LMR240 cable TDoA -> Btw 1 & 3 Btw 1 & 4 Btw 1 & E E E E-5 Std Dev (ns) MSE (ns2) Mean (ns) Variance (ns2) Btw 1 & 2 Results are of average TDoA vector from four runs Expected delay through 100 ft LMR240 cable: 100 ft / ft/ns = ns 29

30 Time Difference of Arrival over 200 ft LMR240 cable TDoA -> Btw 1 & 3 Btw 1 & 4 Btw 1 & E E E E-6 Std Dev (ns) MSE (ns2) Mean (ns) Variance (ns2) Btw 1 & 2 Results are of average TDoA vector from four runs Expected delay through 200 ft LMR240 cable: 200 ft / ft/ns = ns 30

31 Wrapping Up Experiments show our timing variance on 4 different cable lengths (with 4 trials apiece) match expectations RFSNCC allows us to schedule and collect data easily Already collected relatively large (40TB) dataset from stadium 31

32 Contact Github Repo - Hayden Flinner <hayden@gatech.edu> Kristen McClelland <kmcclelland3@gatech.edu> Randal Abler <randal.abler@gatech.edu> Paul Garver <garverp@gatech.edu> Jaison George <jgeorge33@gatech.edu> 32

33 ToA Calculation Simple parabolic interpolation Source: DSPrelated.com 33